Space is always at a premium in commercial vehicles, and the storage of the spare wheel has always been a problem. Placement in a generally horizontal plane underneath the cargo deck presents a lot of interference problems, and any use of the deck area reduces the freight-carrying capacity. This situation has led to the mounting of spare wheels on the front of the vehicle in a generally vertical plane perpendicular to the direction of vehicle movement. Experience has established that a wheel can be placed in this position in front of the radiator without seriously interfering with the cooling air flow if enough space between the wheel and the radiator grille is provided. About a foot of space, in the usual case, appears to be adequate. Such an arrangement, however, obviously provides a structural problem in the support of the wheel. The wheel becomes the most forward point on the vehicle, and thus is the first point contacted by the vehicle in the event of either crash conditions or in pushing other vehicles. In previous mounting arrangements, the carrier has shown an objectionable tendency to fold backward rather easily on contact with any form of obstruction, thus minimizing what would otherwise be a strong safety feature in protecting the frontal area of the truck. It should be noted here that the placement of the spare wheel in a vertical transverse plane has the desirable feature of presenting the side of the tire as the initial contacting surface with any object. While the resilience of this arrangement is desirable, the well-known frictional characteristics of tire material have a tendency to produce a rotation of the spare wheel about a front-rear axis if the tire is contacting the foreign object (as it usually does) at a position below or above the axis, and any relative transverse motion exists between the front of the truck and the object bearing against the front of the spare wheel. This condition is very frequent when a truck is pushing another vehicle. The engagement of the spare wheel with either the bumper of the pushed vehicle or with the tail gate area will produce this type of rotation if there is any lateral shifting of position between the two vehicles.
Pushing or collision forces applied to the spare wheel carrier must be absorbed or dissipated either through (a) resilient deflection of the components, or (b) structural deformation. Where the absorption of energy can take place over a considerable distance, it is obvious that the intensity of the forces involved can be vastly reduced. It would be highly desirable to provide a sufficient energy absorption to keep the forces involved below the point at which permanent deformation of the supporting structure occurred.